We have recently found that the heart of the rat and rabbit contained another type of NAD-linked glycerol-3-P dehydrogenase (GPDH2), which did not cross-react with antibodies directed against pure rat and rabbit liver and skeletal muscle glycerol-3-P dehydrogenase (GPDH1). Our preliminary results show that GPDH1 is the major glycerol-3-P dehydrogenase isoenzyme in liver, kidney, brain, lung, diaphragm, spleen and skeletal muscle, and GPDH1/GPDH2 ratio is approximately 20. In contrast, GPDH1/GPDH2 ratios in rat and rabbit heart were found to be approximately 2 and 0.5, respectively. We would like to know the reasons why the heart, probably vascular system, contains mainly GPDH2, which differs from other tissues. We would also like to know about its roles in cardiovascular structure formation and function. The following experiments will be carried out: 1. Deterination of GPDH1/GPDH2 ratio in the cardiovascular system of various species such as guinea pig, mouse, chick, pig, and dog; 2. Purification of GPDH1 and GPDH2 from the heart and aorta of rabbits and rats; 3. Studies of physicochemical properties of isolated GPDH1 and GPDH2; 4. Studies on catalytic properties (Km, Vmax, Keq, effect of pH, effects of activators and inhibitors); 5. Measurement of GPDH1 and GPDH2 activities in cardiovascular system of the rats and rabbits in various conditions (dietary, hormonal and environmental changes, during heart growth, myocardial hypertrophy, myocardial infarction); 6. Studies on the roles of GPDH1 and GPDH2 in the growth and function of cardiovascular system in normal and pathological circumstances.